This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-276767, filed Sep. 12, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a coating having a high resistance to heat and oxidation and a multi-coated material having a high resistance to heat and oxidation, particularly to the above adapted for use in the manufacture of heat resistant structures such as bodies of space craft and next generation supersonic aircraft, engine parts and gas turbines.
2. Description of the Related Art
When a space craft reentries, a shock wave is generated at the nose tip portion of the body and the leading edge portion of the main wing which leads to high temperatures, with the result that oxygen molecules and nitrogen molecules within the air are dissociated into atomic states. If the dissociated atomic oxygen and nitrogen arrive at the surface of the space craft body, recombination occurs depending on the properties of the surface of the space craft body so as to be brought back to oxygen and nitrogen molecules. The recombination reaction is exothermic and, thus, the surface of the space craft body is heated by both the aerodynamic heating and the heat of the recombination reaction.
The term xe2x80x9ccatalytic propertiesxe2x80x9d denotes the degree of the recombination reaction on the surface of the body of a space craft. The recombination reaction is unlikely to take place on the surface of a material having low catalytic properties and, thus, the temperature elevation on the surface of the space craft body can be suppressed if the above material is used. On the other hand, where the body of the space craft is formed of a material having high catalytic properties, the temperature on the surface of the space craft body is markedly increased because the recombination reaction easily takes place on the surface of the material having high catalytic properties. As a result, a temperature difference of several hundred degrees centigrade is generated between the materials having high and low catalytic properties. Incidentally, this particular phenomenon is inherent in the re-entering environment of space craft.
Vigorous research is being conducted in an attempt to develop a high performance heat resistant system capable of withstanding the aerodynamic heating environment at the time a space craft re-enters the atmosphere.
For example, Yoshinaka, Morino, M. A. Kurtz published various composite materials on page 581 of xe2x80x9cOxidation Behavior of SiC coated Carbon/Carbon Materialxe2x80x9d in the 36th Aircraft Symposium, ""98xe2x80x9d published by Japan Aircraft Space Institute. To be more specific Yoshinaka et. al. published in this symposium various composite materials including a first composite material prepared by forming a SiC layer on a carbon composite material (C/C matrix) by a conversion method, followed by further forming a SiC layer thereon by a CVD method, and a second composite material prepared by applying a SiO2/B2O3 glass seal to the first composite material while clarifying the thermal-chemical erosion mechanism of the C/C matrix consisting of a carbon fiber having a SiC coating applied thereto and a carbon matrix.
Also Nakai, Kinjo, Matsuura, Maekawa, Yumidachi published Japan Composite Material Institute, on page 32 of xe2x80x9cDevelopment of Super High Temperature, Oxidation Resistant, High Strength C/C Composite Materialxe2x80x9d Vol. 19, No. 1, 1993. To be more specific, Nakai et. al. published in this Institute magazine a high temperature oxidation resistant material adapted for use in the manufacture of space craft i.e., the material prepared by forming a carbide layer containing silicon carbide as a main component on the surface of a carbonaceous material, followed by applying a crack seal of SiO2.B2O3 glass material to the carbide layer. The high temperature oxidation resistant material disclosed in this literature exhibits an excellent resistance to oxidation under a high temperature of about 1600xc2x0 C.
However, in the material disclosed in this literature, cracks are generated in the coating because of differences in the thermal expansion coefficient between the coating and the substrate. Also, even if the cracks of the coating are sealed by a glass-based sealing material, the cracks are opened and closed by heating and cooling which takes place when a space craft using the particular material reentries. As a result, the crack seal is thermal-chemically eroded, making it difficult to use the sealed material repeatedly.
On the other hand, Japanese Patent Disclosures (Kokai) Nos. 6-48834 and 7-277861 disclose a high temperature oxidation resistant material prepared by forming an intermediate member containing silicon carbide as a main component on the surface of a carbonaceous material, followed by covering the intermediate member with a composite oxide consisting of an oxide of a lanthanoide series rare earth element and silicon dioxide. The high temperature oxidation resistant material disclosed in these prior arts is superior in its resistance to oxidation at high temperatures over the material previously referred to, and is prepared by forming a carbide layer containing silicon carbide as a main component. To be more specific, the high temperature oxidation resistant material disclosed in the Japanese Patent documents referred to above exhibits an excellent resistance to oxidation under a high temperature of about 1700xc2x0 C.
However, in the above high temperature oxidation resistant material cracks occur in the coating of the composite oxide because of differences in the thermal expansion coefficient between the coating and the substrate. Also, cracks are newly formed in the coating during use of the high temperature oxidation resistance material, as in that of the published literature previously referred to. In addition, the cracks are wider and longer. It follows that the cracks of the coating are not repaired.
Further, the composite oxide coating consisting of the oxide of the lanthanoide series rare earth element and silicon dioxide, which is formed on the surface of the high temperature oxidation resistant material, is certainly excellent in its resistance to oxidation under high temperatures. However, the composite oxide coating noted above tends to have the high catalytic properties referred to previously. As a result, the temperature of the space craft using the particular high temperature oxidation resistant material tends to be markedly elevated by the aerodynamic heating when the space craft reentries during its flight back to the earth.
An object of the present invention is to provide a high temperature oxidation resistant coating composition having a self-repairing function of repairing by itself the cracks under a heating environment and having low catalytic properties.
Another object of the present invention is to provide a high temperature oxidation resistant multi-coated material comprising a high temperature oxidation resistant coating having a self-repairing function of repairing by itself the cracks under a heating environment and having low catalytic properties.
According to a first aspect of the present invention, there is provided a high temperature oxidation resistant coating composition, comprising a glass-based matrix and silicate particles containing a composite oxide consisting of an oxide of a lanthanide series rare earth element including yttrium, and silicon oxide, the silicate particles being dispersed in the glass-based matrix,
wherein the weight ratio of said silicate particles to said glass-based matrix falls within a range of between 40:60 and 90:10.
Further, according to a second aspect of the present invention, there is provided a high temperature oxidation resistant multi-coated material, comprising:
a substrate;
an intermediate layer formed on the surface of the substrate and consisting of at least one ceramic material selected from the group consisting of silicon carbide, silicon nitride, silicon carbonitride, and silicon boride; and
a high temperature oxidation resistant coating formed on the intermediate layer and prepared by dispersing silicate particles containing a composite oxide consisting of an oxide of a lanthanide series rare earth element including yttrium, and a silicon oxide in a glass-based matrix,
wherein the weight ratio of said silicate particles to said glass-based matrix falls within a range of between 40:60 and 90:10.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.